Conventional X-ray computed tomography (CT) apparatus emit X-rays to a subject and detect the X-rays that have passed through the subject to collect projection data, and reconstruct images from the collected projection data. The spatial resolution of a typical X-ray CT apparatus is about 0.35 mm. The spatial resolution of such an X-ray CT apparatus is determined by, for example, pixel size and pixel pitch of a detector and the X-ray focal spot size.
Recent X-ray CT apparatus have been focusing on increasing the maximum resolution. According to a report, some X-ray CT apparatus have achieved the spatial resolution of about 0.12 mm by reducing the pixel size of the detector and/or the X-ray focal spot size, for example. The X-ray CT apparatus usually use the convolution back projection method to reconstruct images, but some X-ray CT apparatus these days use the successive approximation method in reconstructing the images to reduce noise.
In the conventional technology described above, however, the X-ray CT apparatus have, in some cases, difficulty in both preventing an increase in radiation dose and acquiring a high-resolution image of a region that an observer wants to observe.